The invention relates to a passenger restraint system for motor vehicles comprising at least one safety belt on which a belt tensioner is provided; at least one airbag; at least one switch member detecting the functional position of the safety belt and arranged in a belt lock of the safety belt, and at least one sensor that transmits threshold signals, at least in dependence on the effective change of speed of the vehicle, for the activation of the airbag and of the belt tensioner in dependence on the functional position of the safety belt.
A passenger restraint system of this general type is known from German Pat. Specification No. 3,413,768. For protection of the passengers in the event of an accident, that motor vehicle passenger restraint system has safety belts connected to a belt tensioner and at least one inflatable airbag. The passenger restraint system is connected to a control unit having a sensor which activates the individual components of the passenger restraint system in dependence on the effective deceleration of the vehicle. In the presence of a first lower threshold signal of the sensor and with the safety belt fastened, the airbag is not activated. Activation of the airbag occurs only when the second upper threshold signal is transmitted at the sensor. In order to protect the driver effectively and even when the safety belt is not fastened, the first threshold signal is transmitted to the restraint system for causing the release of the airbag. The functional position of the safety belt is detected by a switch member arranged in the belt lock.
In the event of moderate to serious accidents, it has been shown that a fastened shoulder belt can, in some cases, contribute to increasing the risk of injury.
The object on which the invention is based is to design a restraint system of the above general type wherein risk of injury by the shoulder belt is reduced at medium speeds when the airbag is released.
In a restraint system of the relevant generic type, this object is achieved by having an activatable belt-clamping device on the belt lock and an activatable belt pull-out detent for the shoulder belt. Here the sensor transmits at least three different threshold signals. There is a control unit which, when the safety belt is fastened and when the second threshold signal indicating a moderate to serious accident is reached, releases the airbag, arrests the belt-clamping device and releases the belt pull-out detent during the operative period of the airbag and wherein, when the safety belt is fastened and when the third threshold signal indicating a serious accident occurs, arrests the belt pull-out detent. The restraint system according to the invention is based on the knowledge that at medium speeds of between 20 and 50 km/h, the effect of the airbag is sufficient to protect the vehicle passengers in the event of an accident. Therefore, according to the invention, the shoulder belt has an activatable belt pull-out detent which releases the shoulder belt during the operative period of the airbag. During this operative period, the upper body of the vehicle passenger is merely braked by the released airbag. An activatable belt-clamping device is arranged on the belt lock of the safety belt that retains the pelvic region of the vehicle passenger. In this restraint system, there is a sensor which transmits at least three different threshold signals. The first threshold signal is obtained in the event of only minor accidents. The second threshold signal is transmitted in moderate and more serious accidents and the third threshold signal is transmitted in the event of very serious accidents.
If the passenger's safety belt is fastened when the first threshold signal is obtained, there is no activation of the passenger restraint system. In the presence of the second threshold signal and if the vehicle passenger's safety belt is fastened and the airbag is triggered, the shoulder belt is released by means of the activatable belt pull-out detent and the pelvic belt is arrested by means of the activatable belt-clamping device on the belt lock. After an operative period of the airbag, the shoulder belt is once again locked via the belt pull-out detent. In the presence of the third threshold signal and with the vehicle passenger's safety belt fastened, the airbag has already been released in response to the second threshold signal Since the sole effect of the airbag is not sufficient in these accidents, the shoulder belt has to be locked. This is brought about by activating the belt pull-out detent.
In an advantageous embodiment the passenger restraint system is equipped with pelvic-belt and shoulder-belt tensioners separate from one another. In the presence of a second threshold signal in response to which, as stated above, the pelvic belt is fixed by means of the activatable belt-clamping device on the belt lock, an especially good securing of the pelvic region of the vehicle passenger is achieved by means of the pelvic-belt tensioner. After the operative period of the airbag, the belt pull out detent is arrested and at the same time the shoulder-belt tensioner is actuated. The vehicle passenger is thereby protected against a secondary impact.
In another advantageous development the sensor transmits a fourth threshold signal which indicates that the vehicle has overturned. In response to this fourth threshold signal, the control unit is designed so that the pelvic-belt and shoulder-belt tensioners are activated and the belt pull-out detent is arrested. The airbag is consequently not released. If a second threshold signal follows after an overturning (fourth threshold signal), then the shoulder belt remains locked.
In another advantageous embodiment, if the safety belt is not fastened, the airbag is already released when the first threshold signal occurs. The vehicle passenger is thereby protected, in the event of accidents at low speed and with the safety belt not fastened.
It is also advantageous if the belt lock has a first switch contact which, when the safety belt is fastened, breaks a first control line which is connected to an output of the sensor transmitting the first threshold signal to activate the airbag. The switch member possesses further switch contacts which are arranged in further control lines connected to further outputs. To activate the belt pull-out detent of the shoulder belt, there are two flip-flop elements with outputs connected to the belt pull-out detent via an AND element. In a reset state, logically inverted output signals are present at the outputs of the flip-flop elements. The input setting of the first flip-flop element is connected to the second control line and the resetting input of the second flip-flop is activated by means of a timing element. The belt-clamping device is controlled via a third flip-flop element with its input setting connected to the second control line via a control line. The resetting inputs of the first flip-flop element, of the third flip-flop element, and the setting input of the second flip-flop element are activatable by means of a resetting device.